Japanese Sword Arts FAQ Version 2.7
12. Are kendo and iaido dangerous?
Kendo and iaido probably have a lower rate of injury than most martial arts. Kendoka rarely incur injuries worse than a bruise, although there are exceptions of course. Iaidoka have to be extremely careful, especially with shinken (sharp swords), but in general don't get injured very often. Both kendo and iaido are subject to the usual range of strains and soreness to be expected in any sport.
12a. What are the common injuries?
The common injuries in kendo are associated with the feet and ankles. The achilles tendon can be torn, and it is also possible tear the Plantar Fasia muscle (the tensioning muscle on the bottom of the foot). Both injuries can be prevented with a proper stretching program. Less serious but more common is a bruised heel, caused by improper fumikomi-ashi (stamping attack step).
The most common injury in iaido is a cut or pierced left hand. A careless draw with a shinken is likely to severely cut the base of the left thumb. A careless noto (sheathing of the sword) can pierce the hand, even with an iaito.
Iaidoka and kendoka share the hazard of tripping over the hakama, which can cause the usual variety of injuries from falling on a hard surface. Some kendoka and iaidoka can incur chronic wrist injuries, such as carpal tunnel syndrome, from overuse. These are further aggravated if the practisioner also does some other wrist-aggravating activity, such as typing or playing the piano.
A common problem in Iaido is "tennis elbow". This is a pain on the outer side of the forearm muscles, just below or inside the elbow joint. A related problem is "carpal tunnel syndrome" where the other ends of these muscles go under a strap of tissue onto the back of the hand. By using your thumb you can usually find a couple of very painful spots on the elbow, press in and hold or press in and apply friction to all that you can find. Stretch this muscle group by putting your thumb (palm facing out) on your knee and roll your elbow inward with your arm straight. This technique works for both injuries. A pain in the wrist may sometimes be helped by icing the elbow since the pain of a swelled muscle here may be "referring" down into the wrist.
Author's note: I would like to expand this section. Contributions regarding common injuries and prevention schemes appreciated.
12b. Does a shinai blow hurt?
A correct shinai blow which lands on target, ie on the armour, doesn't hurt. You know you've been hit, but there is no pain. A heavy handed cut driven by too much muscle, a typical beginner's stroke, can hurt a bit, more so if the armour is old and soft. The shinai itself is designed to flex and absorb the blow. A cut which misses the armour causes no worse than a bruise, although it certainly can hurt at the time.